In tyre manufacturing, adhesive mixes, commonly known as cements, are normally organic-solvent-based. Adhesive mixes of this sort are highly adhesive and easy to use, mainly on account of rubber dissolving readily in organic solvents and so blending with other rubber to form practically one piece once the organic solvent evaporates.
This type of adhesive mix has the major drawback of containing a large amount of organic solvent, which, as is known, is highly volatile and, because of its characteristics, may pose environmental problems.
For all these reasons, recent European directives have imposed a drastic reduction in the use of organic solvents in tyre manufacturing, thus forcing manufacturers to devise alternative solutions to ensure correct adhesion of rubber layers.
One alternative to conventional adhesive mixes is water-base adhesive mixes. If dried using conventional, i.e. hot-air-circulation, methods, however, applying water-base adhesive mixes has the drawback of taking too long, and of forming a microfilm of water beneath a “dry” surface layer.
One possible solution to the problem is to divide application of the adhesive mix into two consecutive applications, to achieve a very thin layer of adhesive mix at each of the two drying steps. Though dividing application of the adhesive mix into two solves the microfilm formation problem, overall drying time is still longer than for organic-solvent-base adhesive mixes, thus reducing output rate with respect to the latter.